1. Field of the Invention
The invention relates to a volume control method and circuit, and more particularly, to a volume control method and circuit that gradually changes the volume of a signal so as to reduce or eliminate associated noise.
2. Description of the Prior Art
Nearly all audio devices have a volume control located on the user interface. The earliest method to control volume was to instantaneously change the current volume to the destination volume. This method works well for case where the volume difference is nominal. However, in cases where the difference is significant, audio noise is introduced into the volume change, namely in the form of a “popping” noise.
Another method of volume control is given by U.S. Pat. No. 6,535,611 Lau. Instead of instantly changing the volume, U.S. Pat. No. 6,535,611 Lau reaches the destination volume by gradually changing the current volume by a defined incremental value or “volume step” and then passing a certain number of samples wherein a sample corresponds to a certain amount of time. Assume the following for the example: current volume=10, destination volume=20, volume step=2, and sample number=5. The method will check if there is a volume difference present, and if there is, the current volume will be incremented by 2. Afterwards, the method passes 5 samples. Then the process starts again with the method checking if a volume difference is present. As one can see, the method takes 5 increments or volume steps and passes 25 samples to reach the volume destination.
A consequence of this method is that the amount of time it takes to reach the final destination is dependent upon how large the volume difference is. A smaller volume difference results in less samples having to be passed which in turn results in less time used. A larger volume difference results in more samples having to be passed which in turn results in more time used. If the above example had a volume difference of 6, then it would take 3 increments or 15 samples being passed to accomplish the change. If the above example had a volume difference of 20, then it would take 10 increments or 50 samples being passed to accomplish the change.
In addition, the time length of one sample is different for each kind of source material. For example, because the resolution of a CD is smaller than that of a DVD, a sample on a CD is longer than a sample on a DVD. Consequently, a volume change that requires that passing of 25 samples would take longer for CD than a DVD.
Clearly, the methods presented by the prior art have their distinctive drawbacks. Instantaneous change in volume results in an undesirable “popping” noise while gradually changing the volume with a defined incremental value leads to variable times in reaching the final destination for different volume differences.